The invention relates to road paving screeds and methods for supporting and using screeds. In particular, the invention pertains to screeds having changeable widths, and to methods of paving non-coplanar roads.
In the past, it has been desired to have screeds with varying width (otherwise referred to in this specification as the longitudinal dimension) on one or both sides to accomodate paving of road surfaces of varying widths. Most recently, changeable screed width has been accomplished by hydraulically operated extendable mats which can quickly extend up to 5-foot sections of screed at either or both longitudinal ends of the screed, as Barber-Greene Company's Extend-A-Mat commercial product is capable of doing. Such devices also provide for slope control to allow paving of a non-coplanar shoulder at an angle divergent from the main road surface at one side of the main road surface. The commercially available Extend-A-Mat screeds come in an 8-foot model which extends to 15 feet, 6 inches, and a 10-foot model which extends to 19 foot, 6 inches. However, even these dimensions are not adequate for many road paving jobs.
Continued efforts to widen the screed itself, and/or the hydraulically driven Extend-A-Mat sections, have met significant problems. For example, extending the main portion of the screed beyond ten feet creates transportation problems because screeds wider than ten feet cannot easily be moved from one location to another, or may require special wide load permits during transportation. Adding width to the Extend-A-Mat sections, in addition to increasing the overall longitudinal dimension of the screed, create problems of severe stress on the support mechanism of the Extend-A-Mat sections because of the cumulative pressure of the paving material against the extended portions as they are pulled across the road. Furthermore, when one Extend-A-Mat wing is extended while the other one is not extended (or is not as fully extended), the center-line of the longitudinal dimension of the screed including the wing is different from the center-line of the vehicle that distributes the paving material. Accordingly, the feeders which bring material from the paver hoppers will have to provide more paving material to one side than the other. This can result in emptying one side of the paver hopper while the other side has substantial material remaining, thus preventing the hopper from completely emptying. This creates problems in discharging material from dump trucks into the paver hopper.
More recently a West German company, Allgemeine Baumashinen-Gesellschaft (ABC)--Gerhard L. Pottkamper GmbH & Co. KG, has produced a screed which can be extended by insertions of screed sections longitudinally outside of the screed support arms but inside the extendable-mat sections. No provision is made which allows the shifting of the screed widthwise relative to the vehicle nor is the non-symetrical addition of screed sections shown.
It is an object of the present invention to provide a support means allowing for longitudinally shifting of the screed relative to the pulling vehicle.
It is another object of the present invention to provide an improved extendable screed which allows paving a roadway in a single pass even though the crown of the road is divergent from the center-line of the vehicle pulling the screed.
It is yet another object to provide an apparatus and method of paving wherein the division-line of the screed may be shifted so that the paver feeders supplying material to the screed will be feeding more equal volumes of paving material to each side of the screed.
It is further an object of the present invention to provide a screed support system which allows for the support arms of the tractor and the screed to be adequately joined and supported even though the support arms of the screed have been separated by insertion of extension sections.
Other and further objects will become apparent from the following discussion of the invention and its embodiments.